Spark plug



Jan. 8, 1935. J. w. PARKIN. SR

SPARK PLUG Original Filed Feb. 20, 1930 2 Sheets-Sheet l Jan.8,l935.

J. W. PARKIN, SR

SPARK PLUG 2 Sheets-Sheet 2 Original Filed Feb. 20, 1930 Patented Jan.8, 1935 UNITED STATES.

PATENT OFFICE Application February 20, 1930, Serial No. 430,061 RenewedMay 28, 1934 1 Claim.

This. invention relates to spark plugs, and. proposes a novelconstruction based strictly upon scientific and engineering principlesfor adapting the plug to the varying conditions of internal workingtemperature incident to engines of different compression pressure inwhich the plug may be employed; for enabling the exposed parts of theplug to withstand sudden temperature changes such as are encountered inaeroplane practice; for ensuring the plug against beingcontributory todetonation in the cylinder; for improving the sealing of the plug partsagainst compression leakage; for promoting the passage of the spark,particularly in engines of high compression; and for facilitating themanufacture, assemblage, and the selection. and provision of the properplug for a particular .use.

One of the objects of the invention is to provide a spark plugwhi'ch bythe simple interchange of a gasket may be adapted for high, medium, orlow compression internal combustion engines, thus obviating the need ofsupplying special spark plugs for each type. of engine.

Another object of the invention is the provision of a shield for theexposedportion of the porcelain, so disposed and'secured that thepressure thrust of the shield retaining means is transmitted solelythrough the central portion; of the shield, whereby breaking strainsfrom. the center to the periphery ofv the shield are avoided.

A vfurther object of the-inventionis to construct the walls of the flamechamber at the mouth of the plug in such. manner as to secure maximumheat conductivityas well as to protect the ionized spark path betweenthe electrodes, against. deflection, by setting: up a succession ofopposing counter tides to the'inflow of the mixture under the stress ofthe compression stroke, thereby maintaining the body of mixture in theimmediate vicinity of the sparking terminals substantially inert.

Still another object of the invention is the provision of sunken seatsfor the gaskets supporting the insulator, so that the gaskets, onceplaced, be-

come retained in the bushing and, ring-nut respectively, ensuring thecorrect seating and centering of the porcelain each time it may beremoved and replaced, as well as enhancing the sealing efliciency of thegaskets by lengthening the contact surface between said gaskets and theparts which embrace them.

With these and other objects in view the. invention is, disclosed in thefollowing specification and the accompanying drawings in which the samecharacters of reference employed throughout the several figures todenote identical parts.

In the drawings,

Fig. 1 is a view partly in elevation and partly in section showing aspark plug embracing features of the invention and particularly designedfora high compression engine.

Fig. 2 is a longitudinal section through the plug showing a slightlylarger gasket between the porcelain and bushing, adapting the plug to anengine of lower compression.

Fig. 3 is a, bottom plan view of the spark plug.

Fig. 4 is a cross section taken along the line 4-4 of Fig. 2, lookingdownward. v

Fig. 5 is a longitudinal section through the same plug, a thick gasketbeing used, greatly enlarging the combustion space around the insulator,the arrangement being particularly designed for a low compressionengine.

Fig. 6 is a longitudinal section of an intermediate portion of the sparkplug showing a slight modification in the mode and means for seating thegaskets, it being understood that the other features of the plug may bethe same as shown in Figs. 1, 2 and 5.

Fig. '7 is a cross section taken along the line 7-7 of Fig. 6, lookingdownward, the porcelain and gasket being removed.

" Fig. 8 is a longitudinal section of the lower end of the ring-nutshown in Fig. 6, the gasket being omitted.

Before referring in detail to the several figures it may be stated as amatter of known and recognized fact that the higher the compression ofan engine, the higher is the heat value generated at the time ofexplosion. An ordinary spark plug which may work well in a lowcompression engine will therefore fail to work properly in a highcompression engine due to the fact that it becomes overheated at theexplosion temperature of high'compression causing detonation orpreignitlon of the charge.

'On the other hand, while it is highly desirable that the plug should beso designed and constructed as to be free from overheating yet it isessential that it be capable of being heated to the extent that carbondeposits shall not condense upon the insulator.

With regard to overheating of the porcelain it is idle to proposeconducting the heat away from the porcelain for the insulator is at besta poor conductor of heat and no matter how much metal may be made tocontact with the insulator with a view to promoting the dissipation ofheat therefrom, this will relieve the superheated condition of thosesurface areas only, with which the metal makes intimate contact and thecooling of the porcelain by such means is practically negligible. Theonly way in which the porcelain can be effectively prevented frombecoming overheated is to control the access to it of the heated gasesof explosion.

Now adverting to Figs. 1, 2 and 5, the bushing is represented by thereference numeral-'1, in which the insulator 2 is disposed betweengaskets 3 and 4 and held in place by a ring-nut 5 screwing into thebushing into compressive relation to the gaskets and the shouldered zoneof the insulator. It will be noted that in all three of sulator tapersas indicated at 6 and that this tapered portion is surrounded by a wall'7 of the bushing having a corresponding taper so that the sides ofthese corresponding portions ofthe bushing and insulator lie paralleland slightly spaced. In Fig. l the gasket 3 is quite thin, determining anarrow annular combustion space between the insulator and bushing. Thisnot only minimizes the combustion chamber of the cylinder but at thesame time it restricts access of the heated gases of explosion to thesurface of the insulator so' that a'minimum of heat is imparted to theinsulator. This plug is therefore adapted to an engine of highcompression and detonation is avoided by exclusion of the heated gasesfrom the porcelain to the extent that said porcelain shall not becomeheated to the ignition temperature of the compressed mixture. Fig. 2shows the same bushing 1, the same porcelain 2 and'the same portions 6and '7 of corresponding taper. In this plug the thin gasket 3 has beenreplaced by a thicker gasket 8 and in consequence of this substitution,the annular space between the tapered portions of the insulator andbushing is considerably wider than the annular space in Fig. 1. Thiseffect is brought about solely by using a different gasket, and theresult is not only to slightly increase the combustion chamber of theengine, thus determining a lower compression pressure, but to admit alarger volume of the heated explosion gases and thereby permitting theinsulator to become more highly heated than is possible in Fig. 1. Alower cylinder compression can stand a hotter spark plug without risk ofdetonation of the mixture, and a hotter spark plug is desirable in orderto prevent the condensation of carbon upon the insulator.

. Fig. 5 shows'the same plug parts as Figs. 1 and 2 with the exceptionthat a still thicker gasket 9 has been employed between the porcelainand bushing so that the annular space between the tapered portions 6 and7 of. the porcelain and bushing respectively is now quite wide, addingmaterially to the volume of the combustion chamber and at the same timeadmitting a pracferent size according to the prescribed degree ofcompression in connection with which the plug is to be employed. Thishas necessitated the turning out of plugs with different sized bushingsfrom the factory, and the maintaining of stocks of these dilferentlysized plugs by the dealer. The present invention secures the same resultwith identical bushings for spark plugs adapted for every grade ofcompression, merely substituting a difierent gasket, suitable to producethe desired result, in the assembling of the plug. This minimizes thenumber of difierent parts which the factory must-turnout in producingits complete lineof sparkplugs and it materially reduces the stock whichthe'dealer must carry in order to be completely equipped,

for to change from a plug of one compression to that of another it isonly necessary that the the aforesaid figures the lower portion of thein-,,

dealer disassemble the plug he may have on hand, replace it withasuitable thicker or thinner gasketfas the case may be, and thus producea spark plug exactly adapted for the required pur- P Se.

In order further to eliminate the possibility of detonation through-theoverheating of the spark plug that part oithe bushing l which threadsinto thecylinder aperture is made as massive as possible, and providedwith heat diffusing ridges 10 in the mouth of the flame chamber saidridges decreasing in diameter toward the sparking terminals so as togive a general outward flare to the flame chamber. Said ridges'arepreferably acute at their edges andof progressively increasing thicknessso that the heat conductive capacity of said ridges increasesprogressively toward the massive part of the bushing, from which bushingthe heat is carriedaway through the cylinder walls and through thecooling medium in the water jacket provided that the engine is of theliquid cooled type;

The ridges 10 also perform an important function in preventingdisturbance of the spark path between thelectrodes. It is well knownthat a brush discharge immediately precedes the passage of the spark,'-which brush discharge ionizes the gas between the terminals decreasingthe resistance and making it ea'sierfor the spark to jump :the gapp'Itisknow'n also that the ionized gas can readily beblo-wn out of itsrectilinear path, causing arcing of the spark. This increases the lengthof the sp'ark'gap and requires a current of greater voltage to jump thegap. When the tidal flow of mixture, urged by the compression movementof the engine piston sets in toward the spark plug, the mixture impingesagainst'the ridges, setting up concentric eddies or counter-tides whichbuck the infiowing mixture,.reducing the flow velocity of said mixtureand/maintaining the restricted body of mixture in the immediate vicinityof the sparking'termi nals inert, so'that the spark isnot blown into anare but passes substantially rectilinearly, thus requiring a lowervoltage than under ordinary conditions. This is extremely importantsince it is well known that the resistance of the gap increases andbecomes quite enormous in highly compressed mixture.

The gaskets 3, 8 and 9 upon which the insulators are supported in theseveral adaptations of the invention, aswell as the gaskets 4 which sealthe joint between theporcelain and the ring-nut are preferably formed ofmalleable metal such as copperand as shown in Fig. 6 it is preferred toseat them in shallowannular channels. 12 and 13 formed on theconfronting shoulders of the bushing and ring-nut respectively. When thegaskets are first put in place and the ring-nut is screwed tight, thegaskets are spread sufficiently to give them a retaining lit in thechannels in which they are seated. This prevents the gaskets becomingdisplaced when the ring-nut and insulator are removed from the bushing,so that upon replacement of the insulator it will always be correctlyseated and centered. The arrangement of the gaskets within the annularchannels also improves the sealing property of the gaskets bylengthening the area of contact between the gaskets and the bushing andring-nut respectively. It is of course to be understood that thepressure of the ring-nut upon the gaskets conforms them against theinsulator in such manner as to produce a perfect and gas-tight sealbetween said gaskets and insulator.

In order to adapt the spark plug for aeroplane use it is essential thatthe portion of the insulator exposed to the atmosphere must be protectedagainst sudden temperature changes. In making a dive from high altitudewith throttle closed the heated porcelain is suddenly subjected to atemperature drop bringing it down to zero within a few seconds.Contraction stresses are produced by this sudden cooling which commonlycause fracture of the insulator. By the present invention, the exposedend 14 of the insulator is protected by a shield of insulation material15, preferably porcelain. This shield surrounds the central electrode 16and has a shoulder abutting the upper face of the ring-nut, a gasket 17intervening. The shield 15 is spaced from the insulator and inconsequence does not become materially heated. Therefore underconditions of sudden temperature change such as have just been relatedit is not subjected to the injurious strains due to sudden cooling. Anut 18 bears against the upper end of the shield 15 for holding thelatter in place. If the pressure of the nut were transmitted through theshield to the peripheral edge thereof which rests adjacent the upperface of the ring-nut, breaking stresses might be set up in the materialof the shield. In order to prevent this a gasket 19 is placed betweenthe top of the shield and the upper end of the insulator the relation ofwhich to the gasket 17 is such that when the nut 18 is tightened thepressure thrust is transmitted directly through the central portion ofthe shield to the upper end of the insulator so that it may be correctlysaid that the shield rests and is retained upon the upper end of theinsulator and not upon the upper end of the ring-nut. The gasket 17between the peripheral edge of the shield and the ring-nut serves solelyas a packing to prevent access of the outside atmosphere to the outerend of the insulator. A packing gasket 20 may be arranged in an annularspace at the upper end of the shield beneath the nut 18 and surroundingthe central electrode. According to approved practice, the centralelectrode is riveted over the nut 18 as indicated at 21 in Fig. 2 toprevent dislodgment of the insulator.

While I have in the above description disclosed what I believe to be apreferred and practical embodiment of my invention it is to beunderstood that the specific details of construction are merely by wayof example and not to be considered as necessarily limiting the scope ofthe invention.

What I claim as my invention is:

In a spark plug a bushing having a portion of general hour-glass shapehaving bores tapering from both ends toward an intermediate constrictedportion, an insulator seated in said bushing having a portion taperedcorresponding to one of said bores and extending thereinto, forming anannular combustion space, the opposite bore being formed with a seriesof annular parallel ledges facing away from said combustion space and aprogressively diminishing diameter toward the constricted part of saidbushing forming edges lying in the surface of an imaginary cone,tapering towards the interior of the plug. L

JOSEPH W. PARKIN, SR.

